Liquid drop printing or coating system

ABSTRACT

A plurality of liquid drop generators produce adjacent streams of discrete drops toward a moving web. The drops are binarily and selectively charged by charging electrodes located along the path of each drop. Uncharged drops follow their initial trajectory directly into catchers instead of depositing on the web. Charged drops are deflected by a first deflection field which is cyclically varied in discrete steps in a lateral direction, transversely of the web, to several scanned trajectories within a lateral plane, and are then deflected again by a second deflection field in a direction along the path of web travel, thereby causing them to miss the catchers and deposit on the moving web. In one embodiment a scanning control correlates the lateral deflection signals, drop generation, and the movement of the web to control the lateral and longitudinal location of individual deposited drops to form an image or pattern on the web. In another embodiment the web moves intermittently, and during the stationary periods the second deflection field is cyclically varied in discrete steps, correlated to the stepping of the first field, whereby charged drops from each generator can reach appropriate locations within a sub-matrix of the complete image area.

United States Patent 1 1 King 1 I I 1111 3,739,395 1 1 Jime 12, 1973 LllQUllD'DROP PRINTING OR COATING SYSTEM v [75] Inventor: Kenneth 0. King, Rolling Hills,

Calif.

[73] Assignee: The Mead Corporation, Dayton,

Ohio 22 Filed: Oct.12,1971

2.1 Appl. No.: 188,232

[52] us. c1. 346/75 51 Int. (:1. G011! 15/18 [58] Field of Search 346/75, 140, l

[56] I References Cited UNITED STATES PATENTS 3,397,345 '8/1968 Dunlavey 317 3 3,586,907 6/1971 Beam 317/3 3,060,429 10 1962 Winston 346 75 x 3,484,794 12/1969 Winston 346/75 3,500,436 3/1970 Nordin 346/75 Primary Examiner-Joseph W. l-lartary Attorney-Lawrence B. Biebel, Dailey L. Bugg and John W. Donahue et al.

[57] ABSTRACT A plurality of liquid drop generators produce adjacent streams of discrete drops toward a moving web. The drops are binarily and selectively charged by charging electrodes located along the path of each drop. Uncharged drops follow their initial trajectory directly into catchers instead of depositing on the web. Charged drops are deflected by a first deflection field which is cyclically varied .in discrete steps in a lateral direction, transversely of the web, to several scanned trajectories within a lateral plane, and are then deflected again by a second deflection field in adirection along the path of web travel, thereby causing them to miss the catchers and deposit on the moving web. In one embodiment a scanning control correlates the lateral deflection signals, drop generation, and the movement of the web to control the lateral and longitudinal location of individual deposited drops to form an image or pattern on the web. In another embodiment the web moves intermittently, and during the stationary periods the second deflection field is cyclically varied in discrete steps, correlated to the stepping of the first field, whereby charged drops from each generator can reach appropriate locations within a sub-matrix of the complete image area.

1 Claim, 5 Drawing Figures Patented June 12, 1973 3,739,395

SIGNAL SOURCE COUNTER FIG-3 26 28 INVENTOR KENNETH 0. KING 40 MNI BY -Y lOa 50a 50b ATTORNEYS l LEQITID DROP PRINTING OR COATING SYSTEM BACKGROUND OF THE INVENTION In drop printing orcoating apparatus such as disclosed in U.S. Pats. No. 3,373,437 and No. 3,560,641, a plurality of drop generators are provided in a mani fold or head forming an array extending laterally over a receiving surface and expel drops of ink or other liquid toward the surface. The system is stimulated at a common predetermined frequency so all generators form drops of uniform size at a uniform rate, in a fixed phase relationship with the stimulating source.

In such devices, the drops travel toward the receiving surface and are selectively charged in binary fashion according tointelligence signals from a computer, video input, recording tape, etc. The drops to be excluded or caught are electrostatically charged and then pass'through a constant electrostatic deflection field which deflects them from their initial trajectory into catchers, while uncharged drops are deposited, since they are unaffected by the deflection field and follow their initial trajectory onto the receiving surface. i

In printing or coating systems using one or more arrays of drop generators, and in said U.S. Pat. No. 3,560,641, in orderto achieve full coverage of the image area with small drops, it has been proposed to provide a substantial number of arrays of drop genera tors arranged in a staggered fashion such that they track-between each other. The drop control in such arrangements is binary (on-off) but nevertheless the construction is complex both from the mechanical and electrical standpoint! If one drop generator could be arranged to accomplish the function of several, then considerable simplification can be achieved.

In U.S. Pat. No. 3,298,030, a bank of drop generators are'provided, as in FIG. 3 thereof, with the drops at each generator charged to different charge levels depending upon the deflection and displacement desired for deposit of drops from the same generator at different locations. Yet a different charge level is employed to deflect those drops which are not to deposit at all, into a catcher. All drops deflections, for location control or rejection, are generally along the same line, and result from differentcharge levels achieved through changing the voltage level on the same charging electrode.

ln U.S. Pat. No. 3,370,297, it is suggested that a second deflection field" (magnetic) can be applied transversely to the first or normal'constant deflection field. The purpose of this second deflection field is to direct all charged drops, regardless of the magnitude of their charge, into acatcher apparatus, when there is no web or receivingsurface available for the normal printing of a vairiable trace from the drop generator. This secondary reflection will change according to the variable charge on any individual drops, and hence the catcher is constructed as a rather wide element, and the entire arrangement is merely for the purpose of avoiding the deposition of drops or paper in place. v

S UMMARY OF THE INVENTION The present invention is directed to an improved drop printing or coating system and a novel drop means for use therewith. In general, the control 'means disclosed herein charges and deflects only those drops to when there is no receiving surface be deposited on the printing surface, while uncharged drops are caught and thus prevented from depositing. The charged drops are deflected, in two orthogonal directions, causing them to miss the catchers and be de posited on predetermined locations on the printing surface. All charged drops receive an electrostatic charge of the same quantity, thus the system for selecting those drops to be deposited is truly binary and readily operated from a digital information input.

In accordance with preferred embodiments of the in vention, the system includes a plurality of drop generators each having a charging electrode, a first set of deflection electrodes creating a deflection field extending transversely to the direction of travel of the receiving member and positioned below the electrode used to charge the drops binarily. These deflection electrodes are supplied with a common stepped cyclically varying scanning signal which is synchronizedwith drop stimulation, and the field is thus operative to deflect charged drops in a lateral direction across the surface through one of several trajectories.

The drop control means of the present invention also includes second pairs of deflection plates which preferably are positioned below the first deflection plates and establish a deflection field in a second direction across the path of the already deflected chargeddrops. This field operates to deflect the drops in.a longitudinal direction to cause them to pass the catchers and deposit on the printing or receiving surface according to their lateral position, as determined by the first field.

in one embodiment, control circuits correlate the transverse scanning signals (which determine a coordinate position in the lateral direction) with the movement of the drop receiving surface and timing of drop formation (which determines a coordinate position in the longitudinal direction). This transforms input information (which controls only the charging of drops) into an image or characters on the printing surface. in this embodiment the deflection produced by the second deflection plates is constant, and is independent of the scanning or information controls. It merely changes the In another embodiment of the invention, the second deflection electrodes are also subjected to a common stepped cyclically varying scanning signal, correlated to the scanning signal applied to the first sets of electrodes and to drop timing, for producing different deflections of charged drops in the longitudinal direction. Thus charged drops can be deposited in any of a number of matrix or coordinate positions established for each drop generator by the scanning signals. The receiving surface can move continuously, at a slower speed than in the first embodiment, or it can be moved in increments. Thus when each of the generators produces enough drops to fill a complete matrix, then line spacing can occur. Each generator can produce alphanumeric characters within one matrix scan, thus high I speed printing is readily achieved, as well as other graphic displays or designsQ 'In either embodiment the second electrodes, producing a field for longitudinal drop displacement, can be common to all drop generators, since the field produced is either constant, in the first embodiment, or simultaneously cycled for all generators in the second embodiment.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a receiving member such as a web of paper is supplied from a roll 11 over a support table 12 through driving pinch rolls 13 and onto a take-up roll 14. The pinch rolls 13 are continuously driven by a motor 15.

One or more arrays 18, each comprising a plurality of individual drop generators (FIGS. 2 and 3) are positioned over the table 12 in parallel relation, and each generator is adapted to expel a stream of liquid which is broken into individual drops. In the case of a I printing operation, the liquid is ink supplied to each drop generating unit 20 from a pressurized reservoir or ink supplied to all of the arrays 18.

Each of the arrays 18 is provided with a cross passage over an orifice plate 26 for receiving a supply of the stimulated and pressurized ink. The ink is forced through a plurality of small orifices 28 (FIG. 2) to form a plurality of fine streams. The stimulation provided by 4 the vibrator 25 causes all the expelled ink streams to separate into uniformly sized and spaced apart drops 27, directed on parallel trajectories toward the moving web 10. 4 I

Within the arrays each drop generating unit 20 has a vertical passa'ge30 which is aligned with a corresponding orifice 28 and with the trajectory of the expelled drops. A corresponding charge ring 32 is spaced below each orifice 28 at the point of drop separation from the liquid filament extending from the orifice, and applies an electrostatic charge selectively to any individual drop in response to unique binary (on-off) charge signals applied to each charge ring from an information control means, which is described hereafter.

In accordance with the present invention, the uncharged drops are prevented from depositing on the moving web, while the selectively charged drops are deflected in two orthogonal directions before depositing on the moving web. In one preferred embodiment,

each drop generating unit 20 has a first set of deflection electrodes 34 which are supported in parallel relation in the array 18, downstream of the charge ring 32, on opposite sides of the drop trajectory. The deflection electrodes 34 extend in the direction of web travel, and the field created between them, as shown in FIG. 3, will deflect charged drops in the transverse or X direction across the web. Each array 18 is also provided with a second set of deflection electrodes 36 in parallel relation and spaced below the electrodes 34, and extending laterally across the full width of each array 20. As shown in FIG. 3, the passages 30 are preferably enlarged in the lateral direction at a point 38 immediately below the first deflection electrodes 34, and in the region of the second electrodes 36. The field created between the secondelectrodes 36 is generally longitudinal of the web, or in the Y direction.

The charge rings 32 charge only those drops which are to be deposited on the web 10. The selectively uncharged drops, for example drop 27' (FIG. 2), follow parallel straight line trajectories through the passages 30 and into suitable catchers 40 positioned between the web 10 and the corresponding array 18. Each charged drop, on the other hand, is deflected in two directions by the fields from the first and second pairs of deflection electrodes, and one deflection (by the primary pair) causes the charged drops to miss the catcher 40 by deflecting them out. of the plane defined by their original parallel trajectories.

In the embodiment shown in FIGS. 2 and 3 a scan generator 42 is connected through a line 43 to the first deflection electrodes 34 and creates a common cyclically varying scanning deflection field in the X direction across the paths of all of the drops. The output of the scan generator 42 is a signal having a stepped or staircase waveform. As shown by the radiating lines in FIG. 3 a deflected drop may take one of several trajectories on either side of its original path and within a plane parallel to the catcher. The deflecting field created by the plates 34 thus scans the drops laterally but does not affect their descending directly into the catchers 40.

The second deflection plates 36 deflect the selectively charged drops in a second or longitudinal (Y) di- -rection which takes them past the edge of the catcher.

A charged drop, for example drop 27 (FIG. 2), is thereby caused to miss the catcher 40 and deposit on the moving web 10 in accordance with the lateral deflection effected by the first deflection plates 34. In preferred practice, a constant potential is applied from source 44 through line 45 to the second deflection plates 36 and this creates a constant deflection field in the Y direction across the paths of the charged drops which have already been deflected in the X direction,

charge rings 32 through output amplifiers 52and lines 54. The outputs from the control system 50 need only turn on or off the potential applied to the charging electrodes to control which drops will be deflected. This also controls which drops will in fact be deposited because the deflection field in the Y direction is constant and merely causes charged drops to pass the catchers 40. Hence, if an individual drop is not charged it will be caught regardless of the deflection fields established by either of the deflection plates.

The control system 50 also correlates the scanning signals produced by the scan generator 42, the stimulating source 25, and the movement of the web in order to coordinate'placement of the drops on the moving web. Suitable drive controls 56 control the speed of web movement, and the control system 50 actuates these drive controls along with the stimulator 25 which determines the drop formation timing (frequency and phasing), and with the scanning deflection signals created by the scan generator 42. Since the deflection caused by the field between electrodes 36 is constant, the Y coordinate position of individual drops is determined by the constant movement of the web 10.

The control system 50 accordingly establishes a predetermined coordinate position for each drop to be deposited on the web. The drops from each generator, if successively charged, will deflect to adjacent trajectories as they pass through the stepwise increased X- deflection field. Then they will deflect again to avoid the catcher, by the action of the constant or Y- deflection field, and the movement of the web will determine theirposition in this longitudinal direction of the image area. The speed of the web is adjusted whereby transverse lines of deposited drops are successively laid down in longitudinally adjacent rows.

With reference to FIG. 4, another embodiment of the invention incorporates sub-matrix deflection in both the X and Y coordinate directions from the first and second deflection fields. The basic arrangement for each drop generator is the same, hence where appropriate the same reference numerals have been used with the suffix a. Again, only those drops to be deposited on the receiving surface are charged. Charged drops pass through a secondary deflection field created by the electrodes 34a, where they are subjected to a stepwise increasing deflection potential from the scan generator 42a. For purposes of illustration, a 5 X 5 sub-matrix is shown, and in FIG. 5 drops deposited in such a sub-matrix are shown forming the character M. The sub-matrix arrangement is applicable to either embodiment, but it best illustrates the embodiment of FIG. 4.

Instead of the constant deflection potential applied to v the primary electrodes, these electrodes 36a are connected to a further scan generator 44a, which operates at a sub-harmonic frequency of the generator 42a. The wave forms shown within the blocks in FIG. 4 illustrate the principle involved. For each five steps in the output.

as the successive charged drops pass through the varying field created by the electrodes 34a, the first five drops will be deflected into five adjacent trajectories, the same as shown in FIG. 3. These five drops will each pass through the lowest order of deflection field created by the electrodes 36a, thus following the first deflected trajectory 50a in the Y direction to avoid the catcher 40a and deposit on the web a. The second group of five charged drops will be deflected in the same manner in the Y direction, but the intensity of the deflection fields created by the electrodes 36a is now increased by one additional step, and these five drops 6 follow the trajectory identified as 50b. The process 18 repeated an appropriate number of times in order to deflect the charged drops in both the X and Y directions to cover all possible positions of the sub-matrix.

In this embodiment, the web or receiving member can be moved at a speed substantially slower than the Y deflection frequency, such that the movement of the web will have no appreciable effect upon positioning of drops in the Y direction. If such slower constant speed is employed, then the web drive again is controlled ata predetermined constant speed from the control system. It is also possible to move the web 10a in a stepwise direction, whereby the drop generators each cover their appropriate sub-matrices, and the web or sheet is advanced before an additional line of submatrices is scanned. During this time no drops would be charged, and they would in turn project into the catchers. It would be apparent to those skilled in the art that such an arrangement is readily adaptable for use as a line printer or the like, with the charge information for individual characters .or symbols being stored in a memory of the computer incorporated in the control system, according to the particular sub-matrix chosen. Stepwise movement of the web or receiving member 10a can readily be accomplished through the use of stepping motors, or digitally controlled servo systems, if accuracy of line spacing is a desirable feature.

In the arrangement shown and described in connection with FIG. 4, it may be necessary to employ just a single array of drop generators in order to cover the sub-matrix positions desired across the image area on the web or otherreceiving member. In either embodiment, it will be appreciated that the control over which drops are to deposit is a digital binary control, requiring only the charging (or non-charging) of the individual .drops. The stepwise variation of the deflection field or fields is under the control of a common scanning generator, thus the deflection of drops in each of the drop generators can readily be kept in phase and in the same order of magnitude. This is an advantage over systems where the charge level of individual drops must be varied in order to produce appropriate different deflections, since the control arrangementsirivolved here are much simpler. Since the scanning deflection potentials are the same for all corresponding sets of electrodes, the circuits involved areless complex, easier'to construct, and easier to maintain. Both of the above described arrangements show the drops fallingfirst through a cyclically varying transverse electrical field and thence through a longitudinal catch-avoidance field. It is readily apparent that this sequence could be reversed.

While the methods herein described, and the forms of apparatus for carrying these methods into effect,

constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention which is defined in the appended claims.

What is claimed is: 1. A system for controlling the deposit of liquid drops on a receiving member comprising:

means for producing a series of parallel liquid filaments arranged within a common plane, stimulating means for breaking said filaments up into streams of uniformly sized and regularly spaced drops travelling along parallel initial trajectories,

and arranged for longitudinally deflecting said charged drops out of said plane to avoid the catcher and deposit on said receiving member,

means connected commonly to each of said pairs of first deflection electrodes for providing a cyclically varying deflection field therebetween, and

means for moving said receiving member in timed relation with said cyclical variation such that said charged drops are deposited in predetermined matrix locations upon said receiving member. 

1. A system for controlling the deposit of liquid drops on a receiving member comprising: means for producing a series of parallel liquid filaments arranged within a common plane, stimulating means for breaking said filaments up into streams of uniformly sized and regularly spaced drops travelling along parallel initial trajectories, charging means arranged to apply an electrostatic charge of the same magnitude to selected drops within each of said streams, a series of pairs of first deflection electrodes for producing along each of said streams a deflection field which will divert charged drops into laterally deflected trajectories while permitting uncharged drops to continue along their initial trajectories, a common catcher arranged to catch all drops travelling within the plane of said initial trajectories, a common pair of second electrodes located downstream from said pairs of first deflection electrodes and arranged for longitudinally deflecting said charged drops out of said plane to avoid the catcher and deposit on said receiving member, means connected commonly to each of said pairs of first deflection electrodes for providing a cyclically varying deflection field therebetween, and means for moving said receiving member in timed relation with said cyclical variation such that said charged drops are deposited in predetermined matrix locations upon said receiving member. 